A magnetron which is frequently used as an RF wave source has a plurality of anode vanes on its anode. Alternate anode vanes are electrically connected together to form plural resonant cavities, as disclosed in U.S. Pat. No. 3,553,524.
To connect together alternate anode vanes, cutouts are formed at the side fringes of the vanes, and two rings of different diameters are inserted in the cutouts. The rings are joined to the fringes of alternate cutouts in the anode vanes.
FIG. 1 is a plan view of main portions of a conventional magnetron. This magnetron comprises an anode 1, anode vanes 2, 2', a first strap ring 3, a second strap ring 4, and cutouts 5, 5' formed at the fringes of the anode vanes. The anode vanes 2 and 2' extend toward the center 0 from the inner wall of the anode 1. The anode vanes are arranged radially around the axis passing through the center 0. The alternate anode vanes 2 are connected together by the first strap ring 3, while the remaining anode vanes 2' are connected together by the second strap ring 4 that is different in diameter from the first ring 3.
FIGS. 2(a)-2(b) are perspective views of the strap rings. The larger one is the first strap ring 3. The smaller one is the second strap ring 4.
FIGS. 3 and 4 are side elevations of the anode vanes and the strap rings, for showing their connection. FIG. 3 shows the manner in which the anode vanes 2 (only one is shown) are connected together by the smaller second strap ring 4. A cutout 5 is formed at each side fringe of the anode vane 2. One side wall of the cutout 5 is defined by a step 50 over which the second strap ring 4 fits.
FIG. 4 shows the manner in which the anode vanes 2' (only one is shown) are tied together by the larger first strap ring 3. A cutout 5' is formed at each side fringe of the anode vanes 2'. One side wall of the cutout 5' is formed by a step 50'. The first strap ring 3 fits over the step 50'. In this way, the alternate anode vanes 2 are connected together. Also, the alternate anode vanes 2' are connected together.
FIGS. 5(a)-5(b) are perspective view of another known set of strap rings. FIG. 5(a) shows the first strap ring 3, while FIG. 5(b) shows the second strap ring 4. The first ring 3 has the same diameter as the second ring 4. A plurality of outer tongues 3a are formed on the outer periphery at positions corresponding to the positions of alternate anode vanes. The tongues 3a protrude from the outer periphery, and are bent in one direction. Inner tongues 4a are formed on the inner surface of the second strap ring 4 at positions corresponding to the remaining anode vanes. The strap rings 3 and 4 are fitted in the cutouts 5 and 5', respectively, formed in the anode venes 2 and 2', respectively, to couple together alternate anode vanes. The oscillation frequency is determined and the operation is stabilized by adjusting the electrostatic capacitance between the first strap ring and the second strap ring.
In the aforementioned prior art techniques, it is necessary to fabricate the first and second strap rings as separate parts. It is difficult to adjust the oscillation frequency and to stabilize the operation with two strap rings of different diameters or shapes. Further, fabricating two kinds of strap rings increases the cost of the parts.